57 In.H-W 6 1/4 In.L Aluminum Backdraft Damper, Damper Application Backdraft, For Nominal Duct Diameter Not Applicable, Frame Material Aluminum, Number of Panels 2, Maximum Air Velocity 2500 fpm, Overall Height 57 in, Rough Opening Diameter 54 1/4 in, Rough Opening Shape Square, Fits Fan Diameter 54 in, For Duct Shape Not Applicable, Free Area 17 sq ft, Overall Width 57 in, Frame Material Thickness 0.8 in, Overall Length 6 1/4 in, Connection Type Not Applicable, Frame Depth 3 in